How to unify or reconcile quantum mechanics and general relativity is undoubtedly the most important problem in physics. Advances in recent decades suggest that we may have found an important and marvelous clue to the mystery between gravity and quantum mechanics. This clue is successively related to the concepts of the black hole area entropy [1]}, [2]}, [3]}, [4]}, the holographic principle (especially AdS/CFT duality) [5]}, [6]}, [7]}, and the RT formula of the holographic entanglement entropy [8]}, [9]}, [10]}, which have built a bridge between quantum mechanics and general relativity. In particular, the RT formula shows that the entanglement entropy that characterizes quantum entanglement between different parts of a particular class of (i.e., “holographic") quantum systems can be equivalently (i.e., “dually") described by the area of an extremal surface in a corresponding curved spacetime [8]}, [9]}, [10]}.
